A backplane application is a system which can transmit a large volume of data in parallel. It is used in many types of industrial equipment (large-scale hard disk, switchboard, transmission device, measurement equipment, etc.).
Reference number 101 in FIG. 6 represents a conventional backplane application. Said backplane application 101 comprises back board 102 and multiple cards 105.
Back board 102 is made of a thin rectangular substrate. Multiple transmission lines 103 are formed on the back board. Said multiple transmission lines 103 are arranged in the longitudinal direction of back board 102. The transmission lines are arranged in parallel to each other at prescribed intervals. Socket 104 is arranged on back board 102 in such a way that it crosses each transmission line 103. There are multiple sockets 104 which are arranged at prescribed intervals.
Each card 105 has an internal circuit 106, an input/output circuit 110, wiring 121, and a connection part (not shown in the figure). Internal circuit 106 is electrically connected to the connection part via input/output circuit 110 and wiring 121.
Input/output circuit 110 has output circuit 108 and input circuit 109 which are connected back to back. Either output circuit 108 or input circuit 109 is operated under the control of internal circuit 106.
Each card 105 has a signal line group 107 and a connector 118. Internal circuit 106 is connected to an external device (not shown in the figure) via signal line group 107 and connector 118.
In said backplane application 101, one card 105 is inserted into one socket 104. As shown in FIG. 6, each of three cards 105.sub.1 -105.sub.3 are inserted into each of three sockets 104.sub.1 -104.sub.3, respectively.
In this case, the internal circuits 106.sub.1 -106.sub.3 of cards 105.sub.1 -105.sub.3 are electrically connected to each other via the connection parts of cards 105.sub.1 -105.sub.3 and the transmission lines 103 on back board 102.
In said plane application 101, to transfer a signal from internal circuit 106, of card 105, on the output side to internal circuit 106.sub.2 of card 105.sub.2 on the input side, only output circuit 108.sub.1 is switched into the active state in the input/output circuit 110.sub.1 on the output side, and only input circuit 109.sub.2 is switched into the active state in the input/output circuit 110.sub.2 on the input side. When a high-voltage (high-level) signal or low-voltage (low-level) signal is output from output circuit 108.sub.1 on the output side corresponding to the output signal of internal circuit 106.sub.1 on the output side, the signal is output to transmission line 103 via wiring 121.sub.1 on the output side and socket 104.sub.1. The signal is then input from transmission line 103 to internal circuit 106.sub.2 on the input side via socket 104.sub.2 of card 105.sub.2 on the input side, wiring 121.sub.2, and input circuit 109.sub.2.
As described above, the signal is transferred from internal circuit 106.sub.1 on the output side to internal circuit 106.sub.2 on the input side.
In said backplane application 101, one input/output circuit 110 on one card is connected to one transmission line 103. Since multiple input/output circuits 110 are arranged on each card 105, data with the same number of bits as the number of the input/output circuits 110 on a card can be transmitted in parallel among multiple internal circuits 106 in said backplane application 101.
In said backplane application 101, it is required that signals be transmitted as fast as possible between cards 105. As shown in the equivalent circuit diagram illustrated in FIG. 7, terminal resistors 115.sub.1, 115.sub.2, 116.sub.1, and 116.sub.2 are connected in series and arranged at the two ends of transmission line 103.
However, parasitic capacitance is present in said back board 102 and in the wiring of each card 105. Specifically, there is a large parasitic capacitance between input/output circuit 110 of each card 105 and wiring 121 of the socket. Since many cards 105 are installed on back board 102, the total parasitic capacitance of backplane application 101 is very large.
Due to the aforementioned large parasitic capacitance, signals will vary significantly while being transmitted, and the potential of each wiring 121 also varies significantly. Since the potential of each wiring 121 is not stable over a long period of time, it will take a long time for the output of input circuit 109 to settle to either a high level or a low level. As a result, signals cannot be transmitted between output circuit 108 and input circuit 109 at high speed.
To suppress changes in the signal, the resistance values of terminal resistors 115.sub.1, 115.sub.2, 116.sub.1, and 116.sub.2 are reduced. In this case, however, power consumption becomes very high. This is a problem.
The purpose of this invention is to solve the aforementioned problems of the conventional technology by providing a technology which can transmit signals at high speed.